Effective removal of methyl orange and rhodamine B from aqueous solution using furfural industrial processing waste: Furfural residue as an eco-friendly biosorbent

In this study, furfural residue (FR) raw sample as an adsorbent was obtained from the known furfural waste, and without activation by other physical and chemical methods such as activation with metals and/or vapor, carbonization, which was only washed and dried and applied to remove anionic methyl orange (MO) and cationic rhodamine B (RhB) from aqueous solution. Characterization results confirmed that FR exhibited a mesoporous-dominated hierarchical pore structure and was hydrophilic due to abundant oxygen-containing functional groups on the surface of FR, which would be conductive in strengthening the adsorption interaction between dyes and FR. The adsorption mechanism of both dyes was the result of synergistic effects of physical and chemical interactions such as electrostatic interactions, mesopore filling, hydrogen bonds and π-π electron donor-acceptor interactions. The maximum adsorption capacities were 54.95 mg/g for MO and 37.93 mg/g for RhB, which were correspondingly 43.7% and 39.5% higher than most of other biosorbents. The calculated thermodynamic parameters ΔG0, ΔH0, and ΔS0 demonstrated that the adsorption of MO and RhB onto FR was spontaneous and exothermic in the temperature range 293―313 K. More importantly, the adsorbent could be reused for more than five times after simple pretreatment. The findings indicated that FR can be used as an effective, low cost, and eco-friendly adsorbent for dye removal from aqueous solution.